The nail plate is a hard keratinous structure. Its horny cells are cemented together tightly and do not separate, as do stratum corneum cells. Thus, nails can extend indefinitely unless cut or broken. A variety of nail changes can occur in response to systemic and external stresses. For example, prolonged fevers, drug reactions, chemical toxemia and malnutrition may cause the nails to shed altogether, or there may be various degrees of thinning, splitting, ridging or furrowing of the nails. Even emotional stresses may be reflected in abnormal nails. Harsh environmental conditions can cause nails to crack or to become brittle and crack; also, even the use of nail enamel removers can have an adverse effect on the nails. Furthermore, fragile, brittle, thinned or split nails can occur, even in the absence of any discernible abuse.
Over the years, the cosmetic industry has developed and marketed numerous nail treatment products compounded with protein derivatives which are claimed to alleviate the problem of nail brittleness and breakage effecting a large number of women who maintain long nails. U.S. Pat. Nos. 4,402,935; 3,034,965; 4,158,053 and 4,897,261 are all directed to nail treatment products which are applied to the nails and left in place. In U.S. Pat. No. 5,102,654, a nail enamel emulsion composition containing a water phase and a lacquer phase is disclosed. This patent also discloses that vitamins such as panthenol can be incorporated in the product as an optional additive. If used, the panthenol is employed in an amount ranging from about 0.001-0.015 w/w %.
Panthenol, which is an alcohol corresponding to panthothenic acid with vitamin activity, conforms to the formula: ##STR1## has been used rather extensively in hair and skin products for a number of years. For example, U.S. Pat. No. 5,069,898 discloses a hair enrichment composition which contains from 0.005 to 15 weight percent of a hair bulking agent which could include panthenol, biotin, a mucopolysaccharide or mixtures thereof. U.S. Pat. No. 5,445,823 discloses a dermatological composition which contains some panthenol to reduce the skin irritation associated with use of benzoyl peroxide. U.S. Pat. No. 5,425,954 discloses a product which contains panthenol for treating psoriasis. Other patents showing use of panthenol in skin products are U.S. Pat. Nos. 4,721,705; 4,783,332; 5,041,285; 4,595,586; 4,478,853; 4,416,873; 4,863,725; 4,857,321; 4,851,434, and 4,482,537.
There is unpublished information from a supplier of panthenol that panthenol is a useful ingredient in skin care products, particularly hair care products. This information also notes the role of panthenol in nail care products and indicates that when used in a particular manner, it is absorbed into nails and imparts flexibility. This information also includes a report on a study in which a panel of eleven people were subjected to a 0.5% dl-panthenol solution for five days. More specifically, the thumb and third finger of the hand of each person was immersed in the solution to cover the nails for five minutes. This was repeated for five days. The "physiolastic" characteristic of the nails was measured three hours after treatment, and it was concluded that there was a trend for both the rigidity modulus and the viscosity of fingernails to increase after treatment with this solution. Also, this information included a study utilizing nail fragments. In this study, nail flexibility was determined after soaking the fragments in water only. Other nail fragments were soaked in test solutions for 15 minutes, rinsed with water and blotted dry. This was repeated 20 times. The study seemed to show that a solution of 1% panthenol and 1% Triton X-100 improved nail flexibility.